[H⁺] Can Be Determined by the Use of Which Factors

Multiple Choice

[H⁺] can be determined by the use of which factors?
1) HCO₃^-
2) H₂CO₃
3) Inorganic phosphorus
4) PaO₂

A) 1, 2, and 3 only
B) 2 and 3 only
C) 4 only
D) 1 and 2 only